The containers to which the invention more particularly relates are those intended to experience and withstand without appreciable deformation, in use, relatively harsh conditions such as, for example, the filling with a hot liquid and/or the pasteurization of the liquid contained in the container, the filling with a pressurized liquid (for example, carbonated drinks), the cleaning with liquids and/or cleaning agents in the case of reusable containers.
A container of the aforementioned kind is described in Document FR-A-2, 595, 294.
In the first place, it was known how to manufacture containers of this kind which had an outwardly rounded bottom, either hemispherical or of complex shape. However, this shape of the bottom led to the drawback of requiring the addition of a cup enabling the container to rest stably on a support. This additional operation was problematic since it required extra steps, for putting adhesive into place and for centering the cup with respect to the bottom of the container. Furthermore, since there were now two elements made of different materials, this resulted in difficulties with regard to recycling the materials of which the discarded containers were composed. Another drawback of these containers provided with an added cup was that of not withstanding the cleaning operations carried out on reusable containers: the bond between the base and the bottom of the container (by means of an adhesive) deteriorated on contact with cleaning products (for example, sodium hydroxide) and, furthermore, since this bond was not permeable, cleaning or rinsing liquid got into the base and could not be easily removed.
In order to help to overcome these drawbacks, it was attempted to produce bottoms which were rounded the opposite way to the previous ones, with inwardly facing convexity (so-called "champagne bottoms"). However, production of champagne bottoms with a central area having an opposite (outwardly facing) convexity by way of mechanical reinforcement and with a thickness substantially greater (by at least four. times) than that of the side wall of the body, depending on the stresses which the container has to withstand during its use, did not prevent a loss of stability of this bottom, which cracks under the action of the chemical agents used during the cleaning operations and which loses its shape (sinks back in), in particular due to the effect of temperature.